Yusuke Murakami

Toll-like receptor 7 (TLR7) is an endosomal sensor that responds to both pathogen-derived and self-derived single-stranded RNA (ssRNA). Responses of TLR7 to self-derived ssRNA have been implicated in the development of autoimmune diseases, such as systemic lupus erythematosus (SLE). TLR7 antagonists and inhibitory anti-TLR7 monoclonal antibodies (mAbs) can protect lupus-prone NZBWF1 mice from lethal nephritis. However, less is known about TLR7 dependence and activation in human SLE, as both TLR7 and TLR8 respond to ssRNA in humans. Here, we analyzed public databases and found that TLR7 gene signature scores consistently elevated across datasets, races, and SLEDAI scores compared to TLR8, suggesting a deeper involvement of TLR7 in SLE pathogenesis. To specifically inhibit human TLR7 responses, we developed inhibitory mAbs against human TLR7. Utilizing an inhibitory clone, we generated the humanized mAb, DS-7011a. DS-7011a effectively inhibited TLR7-mediated responses in plasmacytoid dendritic cells (pDCs) and B cells. Furthermore, DS-7011a was internalized in a TLR7-dependent manner and accumulated in B cells, pDCs, conventional dendritic cells (cDCs), and monocytes/macrophages. In this study, we describe the generation and preclinical development of DS-7011a, which has the potential to be a therapeutic option for the treatment of SLE.

Although the cause of multiple sclerosis (MS) is not fully known, environmental and lifestyle factors are considered significant risk factors for its development and progression of experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Here, we found that dietary high salt (HS) intake significantly exacerbated the clinical scores of myelin oligodendrocyte glycoprotein-induced EAE mice in the acute phase, but not in the chronic phase. During the acute phase of EAE, HS diet intake selectively promoted neutrophil infiltration into the spinal cord without affecting T cell, B cell, and dendritic cell infiltration. The HS diet-induced exacerbation of clinical scores and microglial activation were improved by the pharmacological inhibition of neutrophil chemotaxis with SB225002, a selective CXC chemokine receptor 2 inhibitor. In addition, the pharmacological inhibition of microglial activation with minocycline markedly ameliorated clinical scores of HS diet-fed EAE mice. Compared with normal diet-fed mice, the levels of thrombin (a serine protease involved in microglial activation) and protease activated receptor 1 (PAR-1), a thrombin receptor, were increased in the spinal cords of the HS diet-fed group. Blockade of thrombin signaling with vorapaxar, a selective blocker of PAR-1, significantly improved EAE symptoms in the HS diet group. Collectively, our findings suggest that excessive salt intake promotes EAE induction via the activation of neutrophils and microglia in the spinal cord. Dietary salt restriction might be a promising strategy to prevent developing or relapsing MS.

Systemic lupus erythematosus is a systemic autoimmune disease characterized by the production of autoantibodies and damage to multiple organs. Glomerulonephritis, a manifestation involving glomerular deposition of immune complexes and complement components, significantly contributes to disease morbidity. Although an endosomal single-stranded RNA sensor [Toll-like receptor 7 (TLR7)] is known to drive glomerulonephritis by promoting autoantibody production in B cells, the contribution of macrophage TLR7 responses to glomerulonephritis remains poorly understood. Here, we have examined Tlr7‒/‒ NZBWF1 (New Zealand Black/New Zealand White F1) mice and found that TLR7 deficiency ameliorates lupus nephritis by abolishing autoantibody production against RNA-associated antigens, C3 deposition, and macrophage accumulation in glomeruli. Furthermore, TLR7 signaling increased CD31 expression on glomerular endothelial cells and Ly6Clow macrophages but not on T and B cells, suggesting that CD31 mediates TLR7-dependent migration of monocytes into glomeruli. Compared to their splenic counterparts, glomerular macrophages produced IL-1β in a TLR7-dependent manner. In addition, single-cell RNA sequencing of glomerular macrophages revealed that TLR7 signaling induced expression of lupus-associated genes, including those encoding Chitinase 3 like 1, ferritin heavy chain 1, IKKε, and complement factor B (CfB). Although serum CfB did not increase in NZBWF1 mice, TLR7-dependent CfB protein expression was detected in glomerular macrophages. In addition, TLR7 signaling promoted C3 cleavage and deposition predominantly on mesangial cells. These findings suggest that TLR7 responses in glomerular macrophages accelerate the progression of glomerulonephritis in NZBWF1 mice.

BACKGROUND: Oxaliplatin, in combination with 5-fluorouracil and leucovorin, is a standard treatment for colorectal cancer and shows high efficacy. However, oxaliplatin induces side effects, such as chemotherapy-induced peripheral neuropathy and myelosuppression, which may lead to dose reduction, temporary drug withdrawal, or discontinuation. Lecithinized superoxide dismutase (PC-SOD) is a drug delivery system formulation with improved blood stability and tissue affinity for SOD. A phase II clinical trial of PC-SOD for chemotherapy-induced peripheral neuropathy has been conducted, and its efficacy has been confirmed for certain parameters. METHODS: In this study, we focused on myelosuppression, a major side effect of oxaliplatin, and aimed to elucidate the preventive effect of PC-SOD in a murine model of myelosuppression. RESULTS: Oxaliplatin administration decreased the white blood cell, platelet, and red blood cell counts and hemoglobin levels in the whole blood of mice. PC-SOD treatment significantly restored the oxaliplatin-dependent reduction in white blood cell count (day 10). The gene expression of cytokines involved in hematopoietic progenitor cell differentiation and proliferation, including colony-stimulating factor (CSF)2, CSF3, interleukin (IL)-3, IL-4, IL-5, IL-6, IL-9, and stem cell factor, was also decreased by oxaliplatin administration. In contrast, PC-SOD treatment markedly restored the gene expression of these cytokines. In vivo imaging analysis showed that oxaliplatin treatment enhanced reactive oxygen species (ROS) production in the femur and tibia, whereas PC-SOD significantly suppressed this production. Furthermore, analysis of mouse-derived bone marrow cells revealed that PC-SOD suppressed oxaliplatin-induced cytotoxicity and ROS production in vitro. CONCLUSION: These results suggest that PC-SOD exerts an antioxidant effect and prevents oxaliplatin-induced myelosuppression, particularly in a murine model of leukopenia.

Nucleic acid (NA)-sensing Toll-like receptors (TLRs) reside in the endosomal compartment of innate immune cells, such as macrophages and dendritic cells. NAs transported to the endosomal compartment are degraded by DNases and RNases. Degradation products, including single-stranded DNA, oligoRNA, and nucleosides, are recognized by TLR7, TLR8, and TLR9 to drive the defense responses against pathogens. NA degradation influences endosomal TLR responses by generating and degrading TLR ligands. TLR ligand accumulation because of impaired NA degradation causes constitutive TLR activation, leading to autoinflammatory and autoimmune diseases. Furthermore, some genes associated with these diseases promote endosomal TLR responses. Therefore, endosomal TLRs are promising therapeutic targets for TLR-mediated inflammatory diseases, and novel drugs targeting TLRs are being developed.

Abstract Eosinophils are typical effector cells associated with type 2 immune responses and play key roles in the pathogenesis of allergic diseases. These cells are activated by various stimuli, such as cytokines, chemokines, and growth factors, but the regulatory mechanisms of eosinophil effector functions remain unclear. Glucocorticoid-induced TNF receptor family-related protein (GITR), a transmembrane protein belonging to the TNF receptor superfamily, is a well-known regulatory molecule for T cell activation. Here, we show that GITR is also constitutively expressed on eosinophils and functions as a co-stimulatory molecule for these cells. Although degranulation was unaffected by GITR engagement of murine bone marrow-derived eosinophils (bmEos), secretion of inflammatory cytokines such as interleukin (IL)-4, IL-6, and IL-13 from IL-33-activated bmEos were augmented by anti-mouse GITR agonistic antibody (DTA-1). In conclusion, our results provide a new regulatory pathway of cytokine secretion from eosinophils where GITR functions as a co-stimulatory molecule.

Toll-like receptor 7 (TLR7) is known for eliciting immunity against single-stranded RNA viruses, and is increased in both human and cigarette smoke (CS)-induced, experimental chronic obstructive pulmonary disease (COPD). Here we show that the severity of CS-induced emphysema and COPD is reduced in TLR7-deficient mice, while inhalation of imiquimod, a TLR7-agonist, induces emphysema without CS exposure. This imiquimod-induced emphysema is reduced in mice deficient in mast cell protease-6, or when wild-type mice are treated with the mast cell stabilizer, cromolyn. Furthermore, therapeutic treatment with anti-TLR7 monoclonal antibody suppresses CS-induced emphysema, experimental COPD and accumulation of pulmonary mast cells in mice. Lastly, TLR7 mRNA is increased in pre-existing datasets from patients with COPD, while TLR7+ mast cells are increased in COPD lungs and associated with severity of COPD. Our results thus support roles for TLR7 in mediating emphysema and COPD through mast cell activity, and may implicate TLR7 as a potential therapeutic target.

Toll-like receptors (TLRs) respond to pathogen constituents, such as microbial lipids and nucleic acids (NAs). TLRs recognize NAs in endosomal compartments. Structural and functional studies have shown that recognition of NAs by TLRs depends on NA processing by RNases and DNases. DNase II-dependent DNA degradation is required for TLR9 responses to single-stranded DNAs, whereas RNase T2-dependent RNA degradation enables TLR7 and TLR8 to respond to nucleosides and oligoribonucleotides. In contrast, RNases and DNases negatively regulate TLR responses by degrading their ligands. RNase T2 negatively regulates TLR3 responses to degrading the TLR3 ligand double-stranded RNAs. Therefore, NA metabolism in the endosomal compartments affects the endosomal TLR responses. Dysregulation of NA metabolism in the endosomal compartment drives the TLR-dependent pathologies in human diseases.

<jats:title>Abstract</jats:title><jats:p>Phospholipase D3 (PLD3) and PLD4 polymorphisms have been associated with several important inflammatory diseases. Here, we show that PLD3 and PLD4 digest ssRNA in addition to ssDNA as reported previously. Moreover, <jats:italic>Pld3</jats:italic><jats:sup>−/−</jats:sup><jats:italic>Pld4</jats:italic><jats:sup>−/−</jats:sup> mice accumulate small ssRNAs and develop spontaneous fatal hemophagocytic lymphohistiocytosis (HLH) characterized by inflammatory liver damage and overproduction of Interferon (IFN)-γ. Pathology is rescued in <jats:italic>Unc93b1</jats:italic><jats:sup>3d/3d</jats:sup><jats:italic>Pld3</jats:italic><jats:sup>−/−</jats:sup><jats:italic>Pld4</jats:italic><jats:sup>−/−</jats:sup> mice, which lack all endosomal TLR signaling; genetic codeficiency or antibody blockade of TLR9 or TLR7 ameliorates disease less effectively, suggesting that both RNA and DNA sensing by TLRs contributes to inflammation. IFN-γ made a minor contribution to pathology. Elevated type I IFN and some other remaining perturbations in <jats:italic>Unc93b1</jats:italic><jats:sup>3d/3d</jats:sup><jats:italic>Pld3</jats:italic><jats:sup>−/−</jats:sup><jats:italic>Pld4</jats:italic><jats:sup>−/−</jats:sup> mice requires STING (<jats:italic>Tmem173</jats:italic>). Our results show that PLD3 and PLD4 regulate both endosomal TLR and cytoplasmic/STING nucleic acid sensing pathways and have implications for the treatment of nucleic acid-driven inflammatory disease.</jats:p>

<jats:p>Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by autoantibody production and multiple organ damage. Toll-like receptor 7 (TLR7), an innate immune RNA sensor expressed in monocytes/macrophages, dendritic cells (DCs), and B cells, promotes disease progression. However, little is known about the cellular mechanisms through which TLR7 drives lupus nephritis. Here, we show that the anti-mouse TLR7 mAb, but not anti-TLR9 mAb, protected lupus-prone NZBWF1 mice from nephritis. The anti-TLR7 mAb reduced IgG deposition in glomeruli by inhibiting the production of autoantibodies to the RNA-associated antigens. We found a disease-associated increase in Ly6C<jats:sup>low</jats:sup> patrolling monocytes that expressed high levels of TLR7 and had upregulated expression of lupus-associated IL-10, CD115, CD31, and TNFSF15 in NZBWF1 mice. Anti-TLR7 mAb abolished this lupus-associated increase in patrolling monocytes in the circulation, spleen, and glomeruli. These results suggested that TLR7 drives autoantibody production and lupus-associated monocytosis in NZBWF1 mice and, that anti-TLR7 mAb is a promising therapeutic tool targeting B cells and monocytes/macrophages.</jats:p>

BACKGROUND: Myeloid differentiation protein-2 (MD-2) is a lipopolysaccharide-binding protein involved in lipopolysaccharide signaling via Toll-like receptor 4 (TLR4). TLR4 plays an essential role in HDM-mediated allergic airway inflammation. Moreover, MD-2 is structurally similar to Der f 2, a major allergen from house dust mite (HDM). OBJECTIVES: We aimed to clarify the role of MD-2 in the pathogenesis of HDM-mediated allergic airway inflammation. METHODS: Wild type (WT), TLR4 knockout, and MD-2 knockout mice were subjected to intranasal instillation of HDM extract, and asthmatic features were evaluated. We also evaluated gene sets regulated by MD-2 in HDM-treated airway epithelial cells and examined the function of dendritic cells from lymph nodes and from lungs. RESULTS: Aggravated allergic airway inflammation with increased airway hyperresponsiveness was observed in MD-2 knockout mice compared with WT and TLR4 knockout mice. Global gene expression analysis revealed an MD-2 regulated proinflammatory response and reconstituted TLR4 signaling in airway epithelial cells. The ability of dendritic cells to evoke an allergic immune response was enhanced in MD-2 knockout mice. CONCLUSIONS & CLINICAL RELEVANCE: MD-2 plays a protective role in HDM-induced airway allergy with the proinflammatory regulation of airway epithelial cells and dendritic cells. MD-2 may serve as a therapeutic target in the treatment of asthma.

Nucleic acid (NA)-sensing Toll-like receptors (TLRs) are synthesized in the endoplasmic reticulum and mature with chaperones, such as Unc93B1 and the protein associated with TLR4 A (PRAT4A)-gp96 complex. The TLR-Unc93B1 complexes move to the endosomal compartment, where proteases such as cathepsins activate their responsiveness through proteolytic cleavage of the extracellular domain of TLRs. Without proteolytic cleavage, ligand-dependent dimerization of NA-sensing TLRs is prevented by the uncleaved loop in the extracellular domains. Additionally, the association of Unc93B1 inhibits ligand-dependent dimerization of TLR3 and TLR9 and, therefore, Unc93B1 is released from these TLRs before dimerization. Ligand-activated NA-sensing TLRs induce the production of proinflammatory cytokines and act on the endosomal compartment to initiate anterograde trafficking to the cell periphery for type I interferon production. In the endosomal compartment, DNA and RNA are degraded by DNases and RNases, respectively, generating degradation products. DNase 2A and RNase T2 generate ligands for TLR9 and TLR8, respectively. In this mechanism, DNases and RNases control innate immune responses to NAs in endosomal compartments. NA-sensing TLRs and the endosomal compartment work together to monitor environmental cues through endosomes and decide to launch innate immune responses.

Stimulator of interferon genes (STING) is a DNA sensor that responds to pathogens and induces type I interferon production. Herein, the role of STING in house dust mite extract (HDM)-induced allergic asthma was investigated. C57BL/6 wild-type (WT) and Sting-/- mice were intratracheally sensitized with HDM, and the bronchoalveolar lavage fluid (BALF), sera, lungs, and mediastinal lymph nodes (MLNs) were analyzed. The total and HDM-specific serum IgE levels were lower in Sting-/- mice than in WT mice. B cell and IgE-positive B cell proportion in BALF and MLNs, respectively, was significantly lower in Sting-/- mice than in WT mice. Additionally, cyclic GMP-AMP, a STING ligand, augmented total and HDM-specific serum IgE levels and B cell proportion in BALF when applied in combination with HDM. To elucidate the role of STING in IgE production, follicular helper T (Tfh) cells, which are involved in B cell maturation, were investigated. Tfh cell proportion in MLNs decreased in Sting-/- mice, and IL-4 and IL-13 production by HDM-restimulated MLN cells from HDM-sensitized mice was decreased in Sting-/- mice compared with WT mice. Thus, STING plays an important role in the maturation and class switching of IgE-producing B cells in allergic inflammation via Tfh cells.

Toll-like receptors (TLRs) impact myeloid cell responsiveness to environmental cues such as pathogen components and metabolites. Although TLR protein expression in monocytes and tissue macrophages is thought to be optimized for microenvironments in each tissue, a comprehensive study has not been reported. We here examined protein expression of endogenous TLRs in tissue-resident myeloid cells. Neutrophils in peripheral blood, spleen, liver and lung expressed TLR2, TLR4 and TLR5 in all tissues. Ly6C+ MHC II‒ classical monocytes mature into Ly6C‒ MHC II+ monocyte-derived dendritic cells (moDCs) or Ly6C‒ MHC II‒ patrolling monocytes. These subsets were found in all the tissues studied. TLR2 and TLR4 were displayed on all of these subsets, regardless of location. In contrast, expression of endosomal TLRs did vary with tissues and subsets. moDCs expressed TLR9, but much less TLR7. In contrast, TLR7, not TLR3 or TLR9, was highly expressed in classical and patrolling monocytes. Tissue macrophages such as red pulp macrophages in the spleen, Kupffer cells in the liver, microglia in the brain, alveolar macrophages in the lung and adipose tissue macrophages all expressed TLR2, TLR4 and TLR3. TLR7 was also expressed in these tissue macrophages except Kupffer cells in the liver. TLR9 expression in tissue macrophages was much lower or hard to detect. These results suggest that expression of endosomal TLRs in myeloid cells is influenced by their differentiation status and tissue-specific microenvironments.

Allergic asthma is one of most famous allergic diseases, which develops lung and airway inflammation. Recent studies have revealed the relationship between the pathology of allergic asthma and the increase of host-derived DNA in inflamed lung, but the role of the DNA-recognizing innate immune receptor for the inflammation is unknown well. Here we investigated the role of Toll-Like Receptor 9 in the pathogenesis of allergic asthma without synthesized CpG-ODNs. To examine that, we analyzed the pathology and immunology of house-dust-mite (HDM)-induced allergic asthma in Tlr9-/- mice and TLR9-inhibitory-antibody-treated mice. In Tlr9-/- mice, airway hyperresponsiveness (AHR) and the number of eosinophils decreased, and production of the Th2 cytokines IL-13, IL-5, and IL-4 was suppressed, compared with in wild-type mice. Interestingly, unlike Th2 cytokine production, IL-17A production was increased in Tlr9-/- mice. Furthermore, production of IL-2, which decreases IL-17A production, was reduced in Tlr9-/- mice. Blockade of TLR9 by treatment with TLR9-inhibitory-antibody, NaR9, effectively suppressed the development of allergic asthma pathology. IL-17A production in NaR9-treated mice was enhanced, which is comparable to Tlr9-/- mice. These results suggest that the TLR9-IL-2 axis plays an important role in Th2 inflammation by modulating IL-17A production in HDM-induced allergic asthma and that targeting of TLR9 might be a novel therapeutic method for allergic asthma.

OBJECTIVE: IgG4-related disease (IgG4-RD) is a unique inflammatory disorder in which Th2 cytokines promote IgG4 production. In addition, recent studies have implicated the Toll-like receptor (TLR) pathway. This study was undertaken to examine the expression of TLRs in salivary glands (SGs) from patients with IgG4-RD. METHODS: SGs from 15 patients with IgG4-RD, 15 patients with Sjögren's syndrome (SS), 10 patients with chronic sialadenitis, and 10 healthy controls were examined histologically. TLR family gene expression (TLR-1 through TLR-10) was analyzed by DNA microarray in the submandibular glands (SMGs). Up-regulation of TLRs was confirmed in SGs from patients with IgG4-RD. Finally, the phenotype of human TLR-7 (huTLR-7)-transgenic C57BL/6 mice was assessed before and after stimulation with TLR agonist. RESULTS: In patients with IgG4-RD, TLR-4, TLR-7, TLR-8, and TLR-9 were overexpressed. Polymerase chain reaction validated the up-regulation of TLR-7 in IgG4-RD compared with the other groups. Immunohistochemical analysis confirmed strong infiltration of TLR-7-positive cells in the SGs of patients with IgG4-RD. Double immunohistochemical staining showed that TLR-7 expression colocalized with CD163+ M2 macrophages. After in vitro stimulation with a TLR-7 agonist, CD163+ M2 macrophages produced higher levels of interleukin-33 (IL-33), which is a Th2-activating cytokine. In huTLR-7-transgenic mice, the focus and fibrosis scores in SMGs, pancreas, and lungs were significantly higher than those in wild-type mice (P < 0.05). Moreover, the concentration of serum IgG, IgG1, and IL-33 in huTLR-7-transgenic mice was distinctly increased upon stimulation with a TLR-7 agonist (P < 0.05). CONCLUSION: TLR-7-expressing M2 macrophages may promote the activation of Th2 immune responses via IL-33 secretion in IgG4-RD.

<title>Abstract</title>A lysosomal transmembrane protein SLC29A3 transports nucleosides from lysosomes to the cytoplasm. Loss-of-function mutations of the SLC29A3 gene cause lysosomal nucleoside storage in monocyte/macrophages, leading to their accumulation called histiocytosis in humans and mice. Little is known, however, about a mechanism behind nucleoside-dependent histiocytosis. TLR7, an innate immune sensors for single stranded RNA, bind and respond to nucleosides. We here show that they drive nucleoside-mediated histiocytosis. Patrolling monocyte/macrophages accumulate in the spleen of <italic>Slc29a3</italic>^−/− mice but not <italic>Slc29a3</italic>^−/−<italic>Tlr7</italic>^−/− mice. Accumulated patrolling monocyte/macrophages stored nucleosides derived from cell corpse. TLR7 was recruited to phagosomes and activated as evidenced by TLR7-dependent phagosomal maturation. TLR7 induced hyper-responsiveness to M-CSF in <italic>Slc29a3</italic>^−/− monocyte/macrophages. These results suggest that TLR7 drives histiocytosis in SLC29A3 disorders. <sec><title>One Sentence Summary</title>SLC29A3 disorders are caused by activation of TLR7 with accumulated nucleosides in lysosomes. </sec>

TLRs respond to a variety of microbial products and initiate defense responses against bacteria and viruses. A variety of pathogens invade into and control the endosomal compartment to survive in host cells. On the other hand, host cells deploy cell surface and endosomal TLRs to pathogen-containing vesicles to mount defense responses. The endosomal compartment is a site for pathogen-sensing. As TLR-dependent defense responses are accompanied with a shift to the anabolic state, TLR responses need to be under metabolic control. Cellular metabolic state is monitored by sensing lysosomal metabolites by the mammalian target of rapamycin complex 1 (mTORC1). Type I IFN production induced by endosomal TLRs requires mTORC1. Recent studies have demonstrated that the interaction between TLRs and mTORC1 depends on their anterograde movement to the cell periphery. In a nutrient-sufficient state, a molecular complex called Ragulator recruits and activates mTORC1 in lysosomes. In parallel, Ragulator allows the small GTPase Arl8b to drive lysosomes to the cell periphery. Nutrient-activated mTORC1 in peripheral lysosomes is constitutively associated with type I IFN signaling molecules such as TRAF3 and IKKα. On the other hand, TLR7 and TLR3 are activated in the endosomal compartment and induce trafficking of TLR-containing vesicles to the cell periphery in a manner dependent on Arl8b or another GTPase Rab7a, respectively. Lysosomal trafficking helps TLR7 and TLR3 to interact with nutrient-activated mTORC1 and type I IFN signaling molecules. The endosomal compartments serve as platforms where metabolic sensing machinery licenses TLRs to initiate type I IFN responses.

TLR3 is a sensor of double-stranded RNA that is indispensable for defense against infection with herpes simplex virus type 1 (HSV-1) in the brain. We found here that TLR3 was required for innate immune responses to HSV-1 in neurons and astrocytes. During infection with HSV-1, TLR3 recruited the metabolic checkpoint kinase complex mTORC2, which led to the induction of chemokines and trafficking of TLR3 to the cell periphery. Such trafficking enabled the activation of molecules (including mTORC1) required for the induction of type I interferons. Intracranial infection of mice with HSV-1 was exacerbated by impairment of TLR3 responses with an inhibitor of mTOR and was significantly 'rescued' by potentiation of TLR3 responses with an agonistic antibody to TLR3. These results suggest that the TLR3-mTORC2 axis might be a therapeutic target through which to combat herpes simplex encephalitis.

Monoclonal antibody (mAb) is an essential tool for the analysis in various fields of biology. In the field of innate immunology, mAbs have been established and used for the study of Toll-like receptors (TLRs), a family of pathogen sensors that induces cytokine production and activate immune responses. TLRs play the role as a frontline of protection against pathogens, whereas excessive activation of TLRs has been implicated in a variety of infectious diseases and inflammatory diseases. For example, TLR7 and TLR9 sense not only pathogen-derived nucleic acids, but also self-derived nucleic acids in noninfectious inflammatory diseases such as systemic lupus erythematosus (SLE) or hepatitis. Consequently, it is important to clarify the molecular mechanisms of TLRs for therapeutic intervention in these diseases. For analysis of the molecular mechanisms of TLRs, mAbs to nucleic acid-sensing TLRs were developed recently. These mAbs revealed that TLR7 and TLR9 are localized also in the plasma membrane, while TLR7 and TLR9 were thought to be localized in endosomes and lysosomes. Among these mAbs, antagonistic mAbs to TLR7 or TLR9 are able to inhibit in vitro responses to synthetic ligands. Furthermore, antagonistic mAbs mitigate inflammatory disorders caused by TLR7 or TLR9 in mice. These results suggest that antagonistic mAbs to nucleic acid-sensing TLRs are a promising tool for therapeutic intervention in inflammatory disorders caused by excessive activation of nucleic acid-sensing TLRs. Here, we summarize the molecular mechanisms of TLRs and recent progresses in the trials targeting TLRs with mAbs to control inflammatory diseases.